The survival and persistence of Nosema locustae Canning in field soils and resident grasshopper populations in Saskatchewan were assessed in a 3-year study. Low levels of N. locustae spores persist in soils but not on vegetation from treated fields. Large numbers of spores were sometimes detected in soil depending on the extent of infection in the resident grasshopper populations. Indigenous soil microorganisms appear to prey upon N. locustae spores or utilize nutrients during spore decomposition. Nosema locustae infection in resident grasshoppers varied, depending on the viability of the spores applied, and its level was higher following repeated (3-year) applications. Low numbers of N. locustae spores persist in soil but large populations probably will not accumulate because of leaching and because of their interaction with soil microorganisms. Spores appeared to leach through soil as a function of water movement.